1. Field of the Invention
The present invention relates to a memory device, and more particularly, to a memory device for writing, storing, and deleting data by inducing magnetic domain wall movement.
2. Description of the Related Art
Due to developments in information technology leading to a requirement for high capacity data storage, demand for data storage media capable of storing large quantities of data continues to increase. Accordingly, data storage speed has been augmented, methods of compacting storage devices have been developed, and as a result, a wide variety of data storage devices has been developed. A widely-used data storage medium is a hard disk drive (HDD), which includes a read/write head and a rotating medium on which data is recorded, and has the capacity for recording 100 gigabytes (GB) of data or more. However, the rotating parts in storage devices such as HDDs have a tendency to wear, so that the reliability of such devices is compromised by the likelihood of a failure during operation after a prolonged period of use.
At present, research and development is underway on a new data storage device that uses a magnetic domain wall movement principle.
FIGS. 1A through 1C are perspective views illustrating a principle of moving a magnetic domain wall. Referring to FIG. 1A, a magnetic wire 10, which includes including a first magnetic domain 11, a second magnetic domain 12, and a magnetic domain wall 13 between the first and second magnetic domains 11 and 12, is illustrated.
A magnetic micro region within a magnetic material will hereinafter be referred to as a magnetic domain. In such a magnetic domain, the rotation of electrons, that is, the direction of the magnetic moment of the electrons is the same. The size and magnetization direction of such a magnetic domain can be adjusted by altering the type of magnetic material, its shape, and size, as well as applied external energy. A magnetic domain wall is a region which separates magnetic domains each having different magnetization directions. Such a magnetic domain wall may be moved or propagated by the application of a magnetic field or a current to a magnetic material.
As illustrated in FIG. 1A, after a plurality of magnetic domains disposed in predetermined directions are created in a magnetic layer with a predetermined width and thickness, the directions of magnetization of the magnetic domains may be reversed using magnetic fields or currents.
Referring to FIG. 1B, when a magnetic field is applied along the magnetic wire 10 in a direction from the second magnetic domain 12 to the first magnetic domain 11, the magnetic domain wall 13 may move in the same direction of the application of the external magnetic field, that is, in the direction from the second magnetic domain 12 toward the first magnetic domain 11. Using the same principle, when a magnetic field is applied in a direction from the first magnetic domain 11 to the second magnetic domain 12, the magnetic domain wall 13 moves in a direction from the first magnetic domain 11 to the second magnetic domain 12.
Referring to FIG. 1C, when an external current is supplied in the direction from the first magnetic domain 11 to the second magnetic domain 12, the magnetic domain wall 13 moves toward the first magnetic domain 11. When a current is supplied, electrons flow in the opposite direction to the direction of the current, and the magnetic domain wall moves in the same direction as the electrons. That is, the magnetic domain wall moves in the direction opposite to that of the externally supplied current. When a current is supplied in a direction from the second magnetic domain 12 to the first magnetic domain 11, the magnetic domain wall moves toward the second magnetic domain 12.
In summary, a magnetic domain wall can be moved using an applied external magnetic field or current, which facilitates the propagation of a magnetic domain.
The principle of moving magnetic domains may be applied to a memory device such as an HDD or a read only memory (RAM). Specifically, it is possible to perform an operation for reading/writing binary data of ‘0’ and ‘1’ by using the principle of changing the magnetic arrangement within a magnetic material by moving a magnetic domain wall of the magnetic material having magnetic domains magnetized in predetermined directions, wherein the magnetic domain walls represents the boundaries between each of the magnetic domains. When a current is applied to a linear magnetic material, the positions of the magnetic domain walls are changed (i.e., the magnetic domain walls propagate) to read and write data, rendering the fabrication of a highly integrated device with a simple structure. Therefore, the principle of moving a magnetic domain wall can be used to fabricate and use memory devices with much larger storage capacities than the conventional memories, such as ferroelectric random access memory (FRAM), magnetoresistive random access memory (MRAM), and phase-change random access memory (PRAM) devices. However, the application of the moving of magnetic domain walls to semiconductor devices is still in the early development stage, and the devices have a comparatively low data storage density. Therefore, there is a need for memory devices employing magnetic domain wall movement with structures optimized for high-density devices.